Modular pump

ABSTRACT

A modular multi-stage pump especially suited for pumping liquids whose external leakage may be hazardous such as liquified gases, including cryogenic fluids, which includes a fully submerged pump and motor unit preferably immersed in a suction pot and sealed with only two external static seals. The unit has a hydrostatic shaft bearing fed with pumpage that also cools the motor and flows back to the first stage discharge. The stages of the pump are in stacked relation and may be increased or decreased in number to develop a desired discharge pressure. The pump and motor unit is encased in a single sleeve casting with a plurality of longitudinal pockets spaced around the periphery thereof housing tubes carrying the pressurized fluids so that the casting is not subjected to the discharge pressure and can be very lightweight. The pump shaft extends through a hollow motor shaft and is keyed to the top end thereof, thereby eliminating a coupling.

United States Patent [191 11] 3,764,236 Carter Oct. 9, 1973 MODULAR PUMP Prima Examiner-William I. Freeh 75It: C.tPd,Clf. men or James Car asa em Assistant Examiner-John F. Wmburn [73]- Assignee: The J. C. Carter Company, Costa Attorneycarlton Hill et a1. Mesa, Calif.

22 Filed: July 15, 1971 [57] ABSTRACT A modular multi-stage pump especially suited for [21] Appl' 162881 pumping liquids whose external leakage may be hazardous such as liquified gases, including cryogenic flu- [52] US. Cl 417/372, 415/104, 415/201, ids, which includes a fully submerged pump and motor Int. Cl. F041) 39/06, F04b 35/04, FOld 3/00 Field of Search 4l5/DIG. 3, 104, 415/201, 501; 417/372, 424, 902

[5 6] References Cited UNITED STATES PATENTS 1,974,678 9/1934 LaFont 417/424 2,419,676 4/1947 Curtis l 415/143 2,450,137 9/1948 Harlamoff.... 417/424 2,900,112 8/1959 Edwards 417/424 2,965,038 12/1960 Purden 417/424 3,135,212 6/1964 Todd 417/424 3,188,967 6/1965 Glessner 415/193 3,199,745 8/1965 Hollis 417/424 3,635,591 l/l972 Wilkinson. 417/424 3,635,599 1/1972 Bryant 417/424 unit preferably immersed in a suction pot and sealed with only two external static seals. The unit has a hydrostatic shaft bearing fed with pumpage that also cools the motor and flows back to the first stage discharge. The stages of the pump are in stacked relation and may be increased or decreased in number to develop a desired discharge pressure. The pump and motor unit is encased in a single sleeve casting with a plurality of longitudinal pockets spaced around the periphery thereof housing tubes carrying the pressurized fluids so that the casting is not subjected to the discharge pressure and can be very lightweight. The pump shaft extends through a hollow motor shaft and is keyed to the top end thereof, thereby eliminating a coupling.

PATENTED 9W3 3,764,236

I N VEN TOR.

MODULAR PUMP BACKGROUND OF THE INVENTION 1. Field of the Invention This invention deals with multi-stage pump and motor units having stacked impellers and diffusers which are easily replaced or omitted to create a desired discharge pressure. Particularly, the invention deals with a modular multi-stage pump suitable for hazardous liquids including liquified gases where pumping stages can be increased or decreased to produce a desired discharge pressure for the assembly.

2. Description of the Prior Art Submerged electric motor-driven pump units for liquified gases are known in the prior art for example in my U.S. Pat. No. 3,369,715 granted Feb. 20, 1968. Multi-stage centrifugal pumps are also known in the prior art, as for example in the Curtis, Aspelin and Carter U. S. Pat. No. 2,660,121 granted Nov. 24, 1953.

SUMMARY OF THE INVENTION According to the present invention, submerged electric motor-driven pump units are now provided with a modular stage assembly that can be increased or decreased as desired to provide the required discharge pressure. The units of this invention are preferably submerged in a suction pot and only two external static seals are needed in the whole assembly. The electric motor and the multiple stage pump are housed in a single open-ended tubular casing enclosed by end caps, one of which also serves as the closure for the suction pot. Fluid such as liquified gas is introduced into the bottom of the suction pot, enters the bottom inlet mouth of the bottom end cap to be acted on by an inducer impeller-flowing the fluid to the first stage of the pump from which it is centrifugally discharged outwardly through a diffuser sleeve where diffuser vanes convert radial flow into axial flow. An overlying cup then directs the axially flowing fluid radially inward to the eye of the next centrifugal impeller. The various stages of the pump are built up from stacked diffuser sleeves and impellers. The last stage of the pump discharges into one or more vertical flow tubes carried in longitudinal pockets spaced circumferentially around the housing so that the housing need not withstand the discharge pressure. The common top cover for the unit and the suction pot has passages registering with the upper ends of the discharge tubes to direct the discharge to a central outlet in the cover.

The pump is driven from a solid shaft depending from the motor shaft which is hollow and through which pumped fluid is circulated for cooling. Some of the pumped fluid also flows through the rotor and stator compartment of the electric motor. The cooling fluid is returned to the first stage of the pump through one or more tubes depending from a pocket in the casing. Some of the cooling fluid flows through a top thrust bearing supporting the pump shaft to eliminate a thrust load on the motor bearings.

Since the top cover is common to both the pump and motor unit and suction pot, a single gasket will seal both the motor unit and the suction pot. A second gassure is maintained on this fluid and even though it is heated it will not gasify under this pressure.

It is then an object of this invention to provide a modular multi-stage cryogenic pump in which stages can be added or subtracted to produce a desired discharge pressure.

Another object of the invention is to provide an electric motor driven multiple stage pump for liquified gases which is submerged in a suction pot, sealed by a cover common to the suction pot and unit and has an internal coolant flow path maintained at least under first stage pumping pressure to prevent gasification when heated.

Another object of the invention is to provide a modular multi-stage pump in which stages can be added or subtracted without change in size or design.

Another object of the invention is to provide a stacked assembly of diffusers and impellers in a multistage pump which can be increased or decreased as desired without changing the overall dimensions of the stack.

A still further object of the invention is to provide an electric motor-driven multiple stage pump where the electric motor has a hollow shaft receiving the pump shaft therethrough, and wherein the pump shaft is suspended from the hollow shaft by a hydrostatic bearing eliminating thrust loads on the motor shaft bearings.

A still further object of the invention is to provide a pump casing with localized pockets receiving discharge tubes to relieve discharge pressure strains from the casing.

Other and further objects of this invention will be apparent to those skilled in this art from the annexed sheets of drawings which, by way of a preferred example only, illustrate one embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view, with a part in vertical section, of a modular multi-stage pump of this invention;

FIG. 2 is a top plan view taken along the line Il-II of FIG. 1;

FIG. 3 is a vertical sectional view taken along the line IIIIII of FIG. 1;

FIG. 4 is a transverse sectional view taken along the line IV-IV of FIG. 1;

FIG. 5 is a transverse sectional view taken along the line V-V of FIG. 3;

FIG. 6 is an enlarged vertical cross sectional detailed view of one pump stage of the pump; and

FIG. 7 is a peripheral elevational view of the diffuser vane cup taken along the line VII-VII of FIG. 6.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 the pump and motor unit 10 of this invention is mounted in a suction pot 11 enclosed by a common cover 12 for both the pump 10 and the pot 11.

The pot 11 has a cylindrical side wall 13, a rounded closed bottom 14, an externally flanged open top 15, a bottom inlet 16 in the side wall thereof close to the bottom 14, and an overflow outlet 17 in the side wall close to the open top 15 thereof and displaced or from the inlet 16.

As shown in FIGS. 3 and 4, the pump and motor unit 10 includes a single sleeve housing 18 preferably in the form of a casting having four radial pockets 19 extending from bottom shoulders or end walls at about the longitudinal mid-point of the sleeve to the top of the sleeve where they terminated at an inturned flange 21 around the open top of the housing. The pockets 19 are preferably disposed 90 apart and are wide enough to accommodate a pair of discharge tubes 22 in side-byside relation extending from an internal end wall 23 closely spaced above the shoulders 20. Thus the sleeve 18 is separated into a top motor compartment 24 and a bottom pump compartment 25 by the end wall 23. As will hereinafter be described, it is not necessary that each pocket 19 receive a pair of tubes 22. At least one of the pockets receives a coolant return tube 26 projecting through the dividing wall 23 into the motor compartment 24 and depending through the shoulder 20 of the selected pocket to a bottom external end flange 27 on the sleeve.

A bottom end cap or cover 28 is secured under the flange 27 and has a depending collar 29 providing an inlet throat 30 for the pump. The cover has a top face 31 diverging from the throat 30 to provide the bottom wall of the first pumping stage 32 in the pumping compartment 25 of the casing 18. ln the illustrated embodiment, four pumping stages 32-35 are provided. Each of these four pumping stages has its own impeller 36, and each, except the top or last stage, has a diffuser sleeve assembly 37 in superimposed relation. The impellers are mounted on a solid pump shaft 38 through wedge collets 39. An inducer impeller 40 is also mounted on the shaft 38 in the throat 30 of the inlet collar 29 at the entrance mouth of the pump. A wedge collet 41 unites the inducer 40 to the bottom end of the shaft 38. A spacer sleeve 42 on the shaft is positioned between the collet 41 and the collet 39 of the first stage impeller 36.

As shown in FIGS. 6 and 7, each diffuser sleeve assembly 37 is composed of a pair of nested cup members 43 and 44. The member 43 has a cylindrical sleeve of flange portion 45 snugly fitting the interior of the casing 18. A top rim portion 46 extends radially inward and axially downward from the top end of the sleeve portion 45 at about a 45 angle and terminates in a depending circular collar 47. This collar 47 surrounds a large diameter circular aperture 48.

The second cup member 44 has a circular sleeve or flange portion 49 nested within the sleeve portion 45 and having circumferentially spaced diffuser vanes 50 therearound. About six vanes are formed on this sleeve portion 49, and each of them provide therebetween passages 51 which curve circumferentially and axially to diffuse flow from the adjacent impeller 36 from a circumferential flow to an axial flow. The gaps 51 open axially at the top of the cup 44.

The cup 44 also has a flat radially extending bottom wall 52 extending inwardly from the bottom of the sleeve wall 49 to an upstanding relatively small diameter circular collar 53 which is a bit larger than the diameter of the pump shaft 38.

A plurality of posts or legs 54 depend from the wall 46 of the cup 43 in spaced concentric relation around the collar 47. Three such posts may be provided.

The cups 43 and 44 are secured together in nested relation by inserting the cup 44 into the cup 43 until its bottom wall 52 is bottomed against the posts 54. Cap screws 55 extend through the bottom wall 52 of the cup 44 and are threaded into the posts 54 to secure the two cups in assembled relation. In such assembled relation the vanes 50 will abut the inner surface of the sleeve or flange 45 so that the diffuser passages 51 are open only at the tops and bottoms thereof being closed on both side faces by the outer flange or sleeve 45 and by the inner flange or sleeve 49. The tops of the passages 51 discharge under the wall 46.

Three diffuser assemblies 37 are used for the four stage pump as shown in FIG. 3 with the outer sleeve 45 of each assembly snugly seated in the casing 18. Pins 56 seated in blind holes in the end faces of adjoining assemblies 37 hold the assemblies against rotation relative to each other. A similar pin 57 is provided between the bottom assembly 37 and the cap 28 to hold the stack against rotation in the sleeve 18. The bottom assembly 37 is supported by the end cap 28.

The collar 53 of each cup 44 carries a bearing 58 rotatably supporting the pump shaft 38.

Each impeller 36 is of the shrouded type having a hub 59 wedge locked on the shaft, a radial top disk portion 60 radiating from the hub 59, a plurality of circumferentially spaced pumping vanes 61 depending from this plate 60 and a shroud 62 overlying the vanes and having a depending collar 63 riding closely inside of the neck 47 of the cup 43. The collar 63 of the bottom impeller 36 rides closely inside of a recess or groove 64 formed in the upper end of the collar portion 29 of the bottom cover 28. The top disk portion 60 of each impeller 36 rides closely under the bottom wall 52 of each cup 44.

The dividing wall 23 of the casing sleeve 18 supports a sleeve 65 which depends into the pumping chamber and carries a radial plate 66 overlying the top impeller of the last pumping stage. This radial plate 66 has a central aperture 67 freely receiving a spacer 68 with a radial flange 68a underlying the plate 66 around the periphery of the aperture 68.

A ball bearing assembly 69 has its outer race slidably mounted in the sleeve 65. A hollow motor shaft 70 projects through the inner race ring of this bearing assembly 69 and has a bottom shoulder 71 resting on the inner race ring.

A drum 72 underlies the inner race ring of the bearing 69 and extends between the spacer 68 and the bottom end of the motor shaft 70.

The upper end of the hollow motor shaft 70 is carried in a ball bearing assembly 73 which has its outer race slidably mounted in a collar 74 depending from the end cover 12. The inner race of this bearing 73 rests on a top shoulder 75 of the motor shaft 70.

Thus, the hollow motor shaft 70 has a bottom shoulder 71 abutted by the inner race ring of the bottom radial bearing 69 and a top shoulder 75 abutting the inner race ring of the top radial bearings 73. The outer race rings of both of the bearings 69 and 73 slide in their respective sleeves so that the motor shaft 70 may rise and fall to the limited extent provided by the extremities of the slide supports for the outer race rings of the bearmgs.

The spacer 68 rotates with the motor shaft 70 while the radial plate 66 remains stationary. When the spacer 68 is in a down position its flange 68a will be spaced below the bottom face of this stationary plate 66 and a gap will be provided for the flow of pumpage from the last pumping stage through the gap 86 surrounding the drum '72 and then through the bearing 69 into the motor compartment. The wider the gap between the flange 68a of the spacer and the bottom face of the plate 66 the more pressure will be exerted against the bottom face of the drum 72 causing the drum to be forced upwardly, raising the motor shaft 70 and relieving thrust loads fromboth of the bearings 69 and 73. If upward thrust loads are present the shaft will be raised closing off the gap and relieving pressure against the drum thereby allowing the shaft to drop downwardly. This arrangement provides a self-compensating thrust balance for the motor shaft and the shaft bearings need only support radial loads.

In addition, a passage 87 is provided through the hub of the top impeller 36 to feed pumpage to the interior of the motor shaft where it will flow through the top of the shaft and thence down through the top bearing 73 into the motor compartment.

Fluid in the motor compartment overflows through the tube 26 into the first pumping stage of the pump where it merges with fluid discharge from the first impeller 36. It will be noted that all heat absorbed by this fluid from pump and motor inefficiencies is delivered to pumped liquid instead of being released back to the inlet which is vented to the supply tank.

The solid pump shaft 38 extends through the top of the hollow motor shaft 70 and a nut 76 is threaded on the extended top end of the pump shaft 38 and is bottomed on a key 77 seated in a slot 78 in the top of the hollow motor shaft 70. The pump shaft 38 is thus suspended from and keyed to the motor shaft 70.

The motor rotor 79 is formed around the motor shaft 70 between the bearings 69 and 73 and is surrounded by the rotor stator 80 mounted in the motor compartment 24 of the casing 18.

Electric wires or conduits 81 extend from the motor through an outlet port 82 provided in the common cap 12 for the pump and motor unit and suction pot.

The cap 12 has four circumferentially spaced radial wing pockets 83 radiating from a central neck 84. These pockets overlie the pockets 19 of the casing 18 and are drilled as at 85 to register with the tubes 22. The drilled holes 85 convey fluid from the tubes 22 into the neck 84 for discharge to the top pump outlet secured on the neck 84. The pockets 83 which are not to be used are not drilled and seal off the open top of an underlying pocket 19.

OPERATION OF THE PUMP Fluid such as liquefied gas or cryogenic fluid is received into the suction pot 11 through the inlet 16 from a source such as a large tank, the hold of a ship or the like. Any of the fluid which is gasified in the suction pot 11 is bled off from the top portion of the suction pot at 17 and may be returned back to the source.

The liquified gas or cryogenic fluid in the bottom of the suction pot l1 enters the open bottom mouth of the bottom end plate 28 and is induced upwardly through the throat 30 into the eye of the first impeller 36. The motor when energized drives the pump shaft 38 to simultaneously rotate all of the impellers 36. Each impeller 36 discharges centrifugally into the passageways provided by the axial diffuser assemblies 37 where the diffuser vanes convert the circumferential flow from the impellers into axial flow to be discharged upwardly and thence radially inwardly to the eye of the next adjacent impeller. After passing successively through the four stages of the pump, the fluid discharged radially from the top impeller 36 enters the bottoms of the discharge tubes 22 in whatever pockets 19 such tubes are mounted. These tubes then empty into the passages 85 in the top cover or lid 12 for discharge into the neck of this lid to an outlet conduit on top of the suction pot.

Some of the fluid from the last or top pumping stage is bled into the hollow motor shaft and also into the bottom of the motor compartment 24 from which it may overflow into the return tube 26 in one of the pockets 19 which tube depends from this pocket to circulate the fluid back to the bottom cover 28 and thence into the discharge from the first centrifugal impeller 36 where it is recirculated back through the second to the fourth pumping stages. Thus all heat from pump and motor inefficiencies absorbed by the recirculated liquid is delivered to the pumped liquid rather then to the suction pot inlet which is in communication with the supply tank and heating of the supply source is prevented.

The pressure from the last pumping stage passes through a throttle orifice provided by the gap between the flange 68a of the spacer and the radial plate 66. Since the motor shaft 70 is free to float axially in the radial bearing supports 69 and 73, a downward thrust or load on the shaft will open up the gap allowing more fluid under pressure to act against the under face of the drum 72 thereby lifting the shaft and closing off the pressure flow. This of course allows the shaft to drop. A self-compensating thrust load relief is thereby provided for the bearings 69 and 73.

If it is desired to inactivate any one or more of the four pumping stages, it is only necessary to remove the impeller from this stage, or if desired to also remove the diffuser assembly 37 and replace it with a dummy spacer sleeve that will support the remaining diffuser assemblies. Thus, a modular design has been provided permitting variable discharge pressures to be maintained as selected by the number of active pumping stages.

From the above descriptions it will therefore be understood that this invention provides a simplified modular multi-stage pump where the number of stages can be varied as desired and wherein an improved sleevetype pump casing houses both the motor and pumping units and cooperates with end covers or caps to maintain the parts in proper operating positions. Only two static seals are needed for the entire assembly. The casing of the combined pump and motor unit can be lightweight and may even be somewhat porous since the discharge pressure is not transmitted to the casing being confined to outlet tubes and end cover passageways. It will also be understood that pumpage used for cooling returns to a pump discharge and is never released to inlet pressures where it might gasify or boil.

I claim as my invention:

1. A pump and motor unit which comprises an open end sleeve housing having an interior dividing wall providing a pump compartment and a motor compartment, localized longitudinally extending pockets spaced circumferentially around the motor compartment portion of the sleeve housing, end caps for the sleeve housing one of which provides an inlet throat to the bottom of the pump compartment and the other of which provides an outlet for pumpage, a motor in the motor compartment having a hollow motor shaft, radial bearings rotatably mounting said hollow motor shaft in the motor compartment, a pump shaft extending from the inlet through the pump compartment and through the hollow motor shaft, means suspending the pump shaft from the top of the hollow motor shaft, means coupling the pump shaft to the motor shaft, a plurality of impellers mounted on the pump shaft in the pump compartment in spaced superimposed relation, a plurality of stacked diffuser cups separating the pumping stages and having diffuser passages receiving the discharge from adjacent impellers, discharge tubes in at least one of said pockets receiving pumpage from the last pumping stage, passageways in the top cover receiving the pumpage from the discharge tubes and conveying the pumpage to the outlet, bleeder passageways between the last pumping stage and the motor compartment and between the last impeller and the hollow pump shaft for bleeding pumpage into the motor compartment to cool the bearings and the motor, one of said pockets having an overflow tube depending therefrom and communicating with the discharge from the first impeller for returning the coolant fluid back to the discharge side of the first stage so as to not relieve the fluid to inlet pressure, and means adapted to be raised by pressure in the last pumping stage for lifting the motor shaft to relieve thrust loads from the motor shaft bearings.

2. The pump and motor unit of claim 1 wherein two discharge tubes are provided in side-by-side relation in at least one of said pockets.

3. The pump and motor unit of claim 1 wherein the overflow tube communicates with the passageway in the end cap having the inlet throat to discharge pumpage from the motor compartment back to the discharge from the first impeller in the pump compartment.

4. A pump and motor unit which comprises an open ended casing sleeve, end covers for the opposite ends of said sleeve, one of said end covers providing a central axial pump inlet, the other of said end covers providing a central axial pump outlet, a dividing wall in said sleeve separating the sleeve into a motor compartment and a pump compartment, circumferentially spaced localized pockets surrounding the motor compartment portion of the sleeve and extending from the pumping compartment to the end of the sleeve, at least one of said pockets having a discharge tube therein communicating with a pumping compartment and with the end cover covering the motor compartment to direct pumpage to the central axial outlet of said cover,

'at least one of said pockets having a tube depending therefrom to the end cover having the pump inlet for circulation of cooling fluid back to the pumping compartment, an electric motor in said motor compartment having a hollow shaft, a shaft extending from the inlet in the end cover through the pumping compartment and through the hollow motor shaft, means coupling the ends of the motor and pump shafts for corotation, a plurality of impellers mounted on the pump shaft in the pump compartment, a plurality of stacked diffuser units in the pump compartment receiving discharge from an underlying impeller and directing the discharge to the next adjacent impeller, bearings carried by the diffuser units rotatably supporting the pump shaft in the pump compartment, an inducer impeller on the end of the pump shaft in the inlet provided by said end cover and means floated by pressure in the last pumping stage acting on the motor shaft to relieve thrust loads therefrom.

5. The pump and motor unit of claim 4 wherein the end cover with the pump outlet has a radial passage therein communicating with the discharge tube.

6. The pump and motor unit of claim 4 wherein the end cover with the pump outlet has a plurality of radial pump portions selectively drilled to provide passageways communicating with the discharge tubes in the pockets.

7. An electric motor driven pump unit which comprises a suction pot, a pump and motor casing sleeve in said pot having a top motor compartment and a bottom pumping compartment, a common lid sealing the top of the suction pot and top of the motor compartment of the sleeve providing an outlet for the pump, a bottom cover on the sleeve in the bottom of the suction pot providing a central axial inlet receiving fluid from the bottom of the pot, a motor in the motor compartment of the sleeve having a hollow shaft, a pump shaft depending from the hollow motor shaft through the pump compartment, a plurality of impellers keyed on the pump shaft in the pump compartment, an inducer keyed on the pump shaft in the inlet of the bottom cover, stacked diffuser units in the pump compartment separating the compartment into a plurality of pumping stages receiving discharge from an underlying impeller and directing the discharge to a superimposed impeller, tubes receiving the discharge from the top pumping stage and feeding the discharge to the common lid for flow to the outlet, another tube conveying coolant fluid from the motor compartment back to the discharge in the first stage of the pump and means operatively connected with said pump shaft acted on by fluid under pressure from said pumping compartment to raise the motor shaft to relieve thrust loads.

8. The unit of claim 7 including a plurality ofimpellers in the pump compartment, a plurality of stacked diffuser units surrounding the impellers for receiving pumpage from an underlying impeller and directing the same to the eye of an overlying impeller, and said diffuser units being selectively increased or decreased in number to vary the discharge pressure of the pump.

9. An electric motor driven pump unit which comprises a casing sleeve providing a top motor compartment with a motor therein and a bottom motor compartment with pumping means therein and an inlet to said pumping means, a shaft coupling said motor and pumping means, a plurality of circumferentially spaced elongated pockets surrounding the motor compartment portion of the sleeve and extending longitudinally along the length thereof, tube means in said pockets for conveying pumpage from the pump compartment to the top of the sleeve, additional tube means depending from one of said pockets on the outside of said pump compartment to communicate pumpage from the motor compartment back to the pump compartment, means operatively connected with said shaft acted on by fluid from said pumping means to raise the shaft for relieving thrust loads, a bleeder passage for pumpage from the top of the pump compartment to the bottom of the motor compartment, and a return passage from the motor compartment back to the bottom of the pump compartment downstream from the inlet to the pump compartment.

10. An electric motor driven pump unit which comprises a casing sleeve providing a top motor compartment with a motor therein and a bottom motor compartment with pumping means therein and an inlet to said pumping means, a shaft coupling said motor and pumping means, a plurality of circumferentially spaced elongated pockets surrounding the motor compartment portion of the sleeve and extending longitudinally along the length thereof, tube means in said pockets for con- 10 ment having a hollow motor shaft, radial bearings supporting the shaft in the motor compartment, a solid pump shaft suspended from the top of the motor shaft, impellers on the pump shaft in the pump compartment, and means for bleeding pumpage from the pump compartment through the hollow motor shaft. 

1. A pump and motor unit which comprises an open end sleeve housing having an interior dividing wall providing a pump compartment and a motor compartment, localized longitudinally extending pockets spaced circumferentially around the motor compartment portion of the sleeve housing, end caps for the sleeve housing one of which provides an inlet throat to the bottom of the pump compartment and the other of which provides an outlet for pumpage, a motor in the motor compartment having a hollow motor shaft, radial bearings rotatably mounting said hollow motor shaft in the motor compartment, a pump shaft extending from the inlet through the pump compartment and through the hollow motor shaft, means suspending the pump shaft from the top of the hollow motor shaft, means coupling the pump shaft to the motor shaft, a plurality of impellers mounted on the pump shaft in the pump compartment in spaced superimposed relation, a plurality of stacked diffuser cups separating the pumping stages and having diffuser passages receiving the discharge from adjacent impellers, discharge tubes in at least one of said pockets receiving pumpage from the last pumping stage, passageways in the top cover receiving the pumpage from the discharge tubes and conveying the pumpage to the outlet, bleeder passageways between the last pumping stage and the motor compartment and between the last impeller and the hollow pump shaft for bleeding pumpage into the motor compartment to cool the bearings and the motor, one of said pockets having an overflow tube depending therefrom and communicating with the discharge from the first impeller for returning the coolant fluid back to the discharge side of the first stage so as to not relieve the fluid to inlet pressure, and means adapted to be raised by pressure in the last pumping stage for lifting the motor shaft to relieve thrust loads from the motor shaft bearings.
 2. The pump and motor unit of claim 1 wherein two discharge tubes are provided in side-by-side relation in at least one of said pockets.
 3. The pump and motor unit of claim 1 wherein the overflow tube communicates with the passageway in the end cap having the inlet throat to discharge pumpage from the motor compartment back to the discharge from the first impeller in the pump compartment.
 4. A pump and motor unit which comprises an open ended casing sleeve, end covers for the opposite ends of said sleeve, one of said end covers providing a central axial pump inlet, the other of said end covers providing a central axial pump outlet, a dividing wall in said sleeve separating the sleeve into a motor compartment and a pump compartment, circumferentially spaced localized pockets surrounding the motor compartment portion of the sleeve and extending from the pumping compartment to the end of the sleeve, at least one of said pockets having a discharge tube therein coMmunicating with a pumping compartment and with the end cover covering the motor compartment to direct pumpage to the central axial outlet of said cover, at least one of said pockets having a tube depending therefrom to the end cover having the pump inlet for circulation of cooling fluid back to the pumping compartment, an electric motor in said motor compartment having a hollow shaft, a shaft extending from the inlet in the end cover through the pumping compartment and through the hollow motor shaft, means coupling the ends of the motor and pump shafts for corotation, a plurality of impellers mounted on the pump shaft in the pump compartment, a plurality of stacked diffuser units in the pump compartment receiving discharge from an underlying impeller and directing the discharge to the next adjacent impeller, bearings carried by the diffuser units rotatably supporting the pump shaft in the pump compartment, an inducer impeller on the end of the pump shaft in the inlet provided by said end cover and means floated by pressure in the last pumping stage acting on the motor shaft to relieve thrust loads therefrom.
 5. The pump and motor unit of claim 4 wherein the end cover with the pump outlet has a radial passage therein communicating with the discharge tube.
 6. The pump and motor unit of claim 4 wherein the end cover with the pump outlet has a plurality of radial pump portions selectively drilled to provide passageways communicating with the discharge tubes in the pockets.
 7. An electric motor driven pump unit which comprises a suction pot, a pump and motor casing sleeve in said pot having a top motor compartment and a bottom pumping compartment, a common lid sealing the top of the suction pot and top of the motor compartment of the sleeve providing an outlet for the pump, a bottom cover on the sleeve in the bottom of the suction pot providing a central axial inlet receiving fluid from the bottom of the pot, a motor in the motor compartment of the sleeve having a hollow shaft, a pump shaft depending from the hollow motor shaft through the pump compartment, a plurality of impellers keyed on the pump shaft in the pump compartment, an inducer keyed on the pump shaft in the inlet of the bottom cover, stacked diffuser units in the pump compartment separating the compartment into a plurality of pumping stages receiving discharge from an underlying impeller and directing the discharge to a superimposed impeller, tubes receiving the discharge from the top pumping stage and feeding the discharge to the common lid for flow to the outlet, another tube conveying coolant fluid from the motor compartment back to the discharge in the first stage of the pump and means operatively connected with said pump shaft acted on by fluid under pressure from said pumping compartment to raise the motor shaft to relieve thrust loads.
 8. The unit of claim 7 including a plurality of impellers in the pump compartment, a plurality of stacked diffuser units surrounding the impellers for receiving pumpage from an underlying impeller and directing the same to the eye of an overlying impeller, and said diffuser units being selectively increased or decreased in number to vary the discharge pressure of the pump.
 9. An electric motor driven pump unit which comprises a casing sleeve providing a top motor compartment with a motor therein and a bottom motor compartment with pumping means therein and an inlet to said pumping means, a shaft coupling said motor and pumping means, a plurality of circumferentially spaced elongated pockets surrounding the motor compartment portion of the sleeve and extending longitudinally along the length thereof, tube means in said pockets for conveying pumpage from the pump compartment to the top of the sleeve, additional tube means depending from one of said pockets on the outside of said pump compartment to communicate pumpage from the motor compartment back to the pump compartment, means operatively connected with said shaft acted on by fluid from said pumping means to raIse the shaft for relieving thrust loads, a bleeder passage for pumpage from the top of the pump compartment to the bottom of the motor compartment, and a return passage from the motor compartment back to the bottom of the pump compartment downstream from the inlet to the pump compartment.
 10. An electric motor driven pump unit which comprises a casing sleeve providing a top motor compartment with a motor therein and a bottom motor compartment with pumping means therein and an inlet to said pumping means, a shaft coupling said motor and pumping means, a plurality of circumferentially spaced elongated pockets surrounding the motor compartment portion of the sleeve and extending longitudinally along the length thereof, tube means in said pockets for conveying pumpage from the pump compartment to the top of the sleeve, additional tube means depending from one of said pockets on the outside of said pump compartment to communicate pumpage from the motor compartment back to the pump compartment, means operatively connected with said shaft acted on by fluid from said pumping means to raise the shaft for relieving thrust loads, said motor in the motor compartment having a hollow motor shaft, radial bearings supporting the shaft in the motor compartment, a solid pump shaft suspended from the top of the motor shaft, impellers on the pump shaft in the pump compartment, and means for bleeding pumpage from the pump compartment through the hollow motor shaft. 